Nowadays, scene or show projectors are constituted by a light source constituted for example by a bulb, a discharge or incandescent lamp or still by monochromatic or polychromatic light-emitting diodes in order to obtain a color or a range of colors by additive synthesis. In the case of projectors provided with light-emitting diodes, the projectors are provided, to this end, with a (parabolic or elliptical) reflector for collimating the light beam coming from this light source toward a Köhler (Koehler) integrator for example thereby enabling an additive synthesis of the wavelengths comprised in the beams of light rays.
This additive synthesis phenomenon is perceived by the human eye by means of photoreceptors present in the retina: the cones. In general, these photoreceptors are divided into three types of cones and each of the types has sensitivity to a range of wavelengths. Thus, a better perception of colors is enabled to humans. Of course, the term «synthesis» is an abuse of language or, in other words, the colors mixture process takes place only in the brain. Anyway, this additive synthesis creates the illusion of a given color.
In practice, the collimators forming the related art are designed to shape the light beams of the light-emitting diodes, better known by the acronym «LED», and, in particular, the light beams of multi-chip Red, Green and Blue LEDs, also called RGB LEDs. In general, a White chip is associated to the Red, Green and Blue chips. This last configuration, called LED RGBW, enables a more nuanced and rich color synthesis. The collimators adapted to RGBW LEDs according to the related art comprise a central portion architected so as not to form the image of the chip using a set of confocal diopters for example and a peripheral portion configured so as to divert the light toward a network of micro-lenses for example in order to improve the rendering.
The central portion of a collimator adapted to RGBW LEDs according to related art places restrictions on the entire geometry of the collimator, on the size of the LED and on the angle of the projected beam. Thus, the geometry of a collimator adapted to RGBW LEDs according to the related art is bulkier than that of a conventional collimator provided for a white LED. A collimator adapted to RGBW LEDs according to the related art operates in an optimal manner only for one single size of LEDs, and the angle of the projected beam, in particular the angle of the beam projected by the central portion, is larger than the asymptote defined by the throughput sources.
Hence, there is a need for an optical system allowing providing a uniform and homogenous colors mixture from an RGBW LED, while guaranteeing the smallest possible throughput sources, in order to reduce as much as possible the angle of the projected light beam.